1. Field of the Invention
This invention relates to solar panels for heating water. More particularly, it relates to a solar panel having a structure that provides hotter water than similar panels but which prevents over-heating.
2. Description of the Prior Art
Conventional solar panels include a collection of parallel pipes having their opposite ends collectively in fluid communication with an inlet manifold and an outlet manifold. The water is heated by solar radiation as it travels through the pipes from the first manifold to the second manifold.
In a simple installation, the pipes are exposed to the ventilating effect of the ambient environment. As a result, the water temperature rarely exceeds one hundred twenty degrees Fahrenheit (120° F.). This may be unacceptably cool for some applications such as cold swimming pools. In such cases, a higher temperature is desirable.
Inventors have therefore applied glazing to the pipes to make them absorb greater amounts of heat.
If a solar panel is made of metallic tubing, the structural integrity of the tubing is substantially unaffected by the elevated water temperatures made possible by glazing, which temperatures may be about one hundred eighty degrees Fahrenheit (180° F.). The water can be dangerously hot if used for a hot water heater, for example.
Where plastic tubing is used, over-heating can be a problem because the water temperature may approach or exceed the degradation temperature of the plastic. Still, plastic tubing is desirable due to its low weight, relatively low cost, elimination of calcification and scaling of the tubes, and high heat transfer efficiency.
Glazing is thus understood as solving the low-temperature problem and creating an over-heating problem.
Another technique for producing hotter water includes covering the pipes with materials that allow solar radiation to pass therethrough but which block air flow over the pipes to prevent cooling by natural ventilation. This solution has the same shortcoming as glazing in that it can produce water that is too hot.
Thus there is a need for a structure that enables a solar panel made of plastic tubing to attain temperatures higher than one hundred twenty degrees Fahrenheit (120° F.), but lower than dangerously hot temperatures, and which protects the plastic tubing from over-heating.
However, in view of the prior art taken as a whole at the time the present invention was made, it was not obvious to those of ordinary skill how the identified needs could be fulfilled.